1. Field of the Invention
The present invention relates to circuit devices for implementing a generator of highly pure signals. More specifically, the present invention relates to a frequency synthesizer for providing highly pure signals in which noise is suppressed as low as possible and spurious components are rejected as far as possible and circuit devices, such as a voltage controlled oscillator (VCO), a phase locked loop (PLL) and a signal generator (SG), which are used in the frequency synthesizer.
2. Description of the Related Art
Recent synthesized signal generators for a quasi-microwave region of, for example, 10 KHz to 2,700 MHz are requested not only to be multifunctional but also to suppress SSB phase noise (C/N) as low as possible in order to implement a generator of highly pure signals.
To this end, a set of circuit devices, such as a frequency synthesizer, a VCO, a PLL, (a SG,) a mixer and a frequency and phase detector, which are used in a synthesized signal generator must be configured to be effective in suppressing noise individually or in combination. Moreover, the set of circuit devices must be configured to meet requirements for low noise, miniaturization and simplification.
However conventional frequency synthesizers using a PLL and other circuit devices have not been configured yet to meet such requirements.
Hereinafter, prior arts of the circuit devices and their problems will be described.